1. Field of the Invention
The present invention relates to a throttle valve controller and, more particularly, to a throttle valve controller for an internal combustion engine that is used to finely control the intake air quantity when the internal combustion engine is in an idling state.
2. Description of the Prior Art
When an internal combustion engine for an automobile is in an idling state in particular, the intake air quantity is affected considerably by environmental or equipment temperature or other conditions. Therefore, it is necessary to finely control the intake air quantity. Various techniques of finely controlling the intake air quantity have already been proposed.
Examples of the proposed techniques are as follows:
1 Japanese Patent Application Post-Examination Publication No. 5-34518 is an example of a bypass air valve system that controls a bypass air passage provided in parallel to the throttle valve. The publication discloses a system that uses a rotary solenoid valve.
2 Japanese Patent Application Unexamined Publication (KOKAI) No. 3-107544 is an example of a direct-acting system that directly drives the throttle valve only in a small throttle opening range. The publication discloses a system in which the throttle valve is driven by a DC motor.
3 Japanese Patent Application No. 10-69410 is an example of a DBW (Drive By Wire) system in which the throttle valve is driven in the entire throttle opening range by using various actuators. Japanese Patent Application No. 10-69410 employs a torque motor as an actuator.
In the above-described various systems, the bypass air valve system stated in 1 generally adopts open-loop control and hence suffers from problems in terms of accuracy. To adopt closed-loop control, a position sensor is additionally needed, resulting in an increase in cost.
The direct-acting system stated in 2 drives the throttle valve by a DC motor and therefore requires speed reduction through a gear mechanism to obtain appropriate control resolution owing to the transmission structure thereof. Accordingly, this system suffers from problems in terms of response due to speed reduction as well as an increase in cost.
In the DBW system stated in 1, no matter which actuator is used, i.e. a torque motor, a DC motor, or a stepper motor, the cost of the actuator unavoidably increases to obtain satisfactory driving force and driving range. In addition, higher levels of fail-safe and limp-home capabilities are demanded. Accordingly, the system becomes unfavorably costly.